Place butter in the freezer for at least 60 minutes.

Preheat oven to 450° F with a rack in the upper third of the oven. Line a baking sheet with parchment paper.

In a large bowl, combine the flour, baking powder, sugar and salt. Whisk together until well combined.

Grate the frozen butter using a box grater. Add the butter to the bowl and use a fork to mix it into the dry ingredients. Use a fine box or place grater. You want small pieces.

Pour the 1 cup milk or buttermilk (with the sour cream blended in) into the bowl and use a fork to stir until the dough comes together. It is ok if there are a few bits of flour not yet incorporated, but if the dough seems very dry and is not coming together add 1 to 2 tablespoons more milk or buttermilk. (I tend to figure this out when I start to laminate the dough. You can just use a pastry brush to LIGHTLY moisten the dry spots)

Turn the dough out onto a lightly floured work surface. Pat the dough into a 1½-inch thick rectangle. Fold the dough in thirds on top of itself and pat it down into another 1½-inch thick rectangle. Repeat the folding process 4 to 6 times. Then press the dough down into a 1-inch thick rectangle.

Use a biscuit cutter (mine measures 2 ¼-inches) to cut out the biscuits, pressing it straight down into the dough without twisting. Once you've cut out as many biscuits as you can, gather the scraps and pat the dough out to 1-inch thickness a second and third time to finish cutting out all of the biscuits. Place them on the prepared baking sheet. Trim the folded edges of dough with a lame or sharp blade. Otherwise your spring will be uneven.

If desired, brush the biscuit tops with milk, buttermilk, cream or melted butter. Bake for 13 to 16 minutes, until the tops are lightly golden brown.